indeed Jim its a shame when gross inaccuracies in books or in even nowadays internet articles, that are are used to inflate the prices of junk pieces...
Chaps, the crown on the lead stamp is for the last 2 century's at least a Queens crown not a Kings, Its either Vickys or Lizzies, but as it is stamped in lead in reverse, from a true stamp it clearly, not an old British museum stamp. {Even impoverished carpenters had there own steel stamps made, to mark there tools in Victorian times, never mind museums!}
More like an impression made from a Crown button, buckle or some such. Cold pressed into a piece of soft lead.
Spiral